1. Field of the Invention
The present invention concerns a procedure for the application of a PTFE (polytetrafluoroethylene)-based, self-lubricating coating on a bearing element whose surface comes into contact with other surfaces by rolling or sliding. It further concerns the bearings thus obtained.
2. Discussion of the Background
U.S. Pat. No. 3,414,084 describes a well-known procedure for applying a self-lubricating coating based on PTFE in powder form, which is applied in particular to ball and roller bearings. This procedure involves blowing a PTFE-based powder into a bearing while rotating said bearing, so as to fill the interstices inside the bearing. This procedure is long and complex. Furthermore, it is difficult to achieve the fluid-tightness of the bearing. A higher degree of corrosion protection is obtained by increasing the quantity, and thus the thickness, of the PTFE coating on the internal surfaces of the bearing by increasing the roughness of these surface, either by mechanical or by chemical and electrochemical means. However, the increased thickness of the coating resulting from the abrasion of the surface eliminates the advantages of a thin coat application, which allows the bearing to function under high contact pressures without separation or tearing away of the PTFE layer from its base.
FR-A 2 082 623 describes a PTFE-coating procedure performed using electrophoresis on underlayers containing phosphates or on other underlayers formed using electrophoresis. The steps in the procedure, including cleaning, electrolytic scouring, coating by means of electrolysis, all of which are intrinsic to electrolytic procedures, increase the fragility of the treated components, and especially the steel subjected to rolling.